[DAGCombine]: Fold X/Sqrt(X) to Sqrt(X)

With FMF ( "nsz" and " reassoc") fold X/Sqrt(X) to Sqrt(X).

This is done after targets have the chance to produce a
reciprocal sqrt estimate sequence because that expansion
is probably more efficient than an expansion of a
non-reciprocal sqrt. That is also why we deferred doing
this transform in IR (D85709).

Differential Revision: https://reviews.llvm.org/D86403